After he was sworn in, the head of the country's election commission handed him a card identifying him as the President of Belarus.
The ceremony was held in front of several hundred dignitaries at the Palace of Independence in the capital of Minsk today. Law enforcement officers blocked off central areas of Minsk on Wednesday morning and public transportation services were suspended.
Mr Lukashenko's abrupt inauguration has been denounced as illegitimate by opposition leaders who have called for more protests against his controversial landslide victory in an election critics and several foreign governments insist was rigged.
"This is the day of our wonderful victory", he said.
The EU is preparing sanctions against around 40 people deemed responsible for the repression and also looking at punishing Lukashenko himself, diplomatic sources say. The EU believes that the results of the August 9 polls, which handed President Alexander Lukashenko his sixth term with 80% of the vote, "have been falsified", and the 27-nation bloc is preparing a list of Belarus officials who could be blacklisted from Europe over their roles.
Tikhanovskaya, who is in exile in neighboring Lithuania where she was forced to flee after the election, was given just 9% of the vote by the official count during it, widely viewed as vastly underestimating the real result. His strongest opponent, Sviatlana Tsikhanouskaya, got 10 percent.
Russian Federation is a close ally of Belarus and defence analysts said the "Slavic Brotherhood" military exercises were an overt display of muscle-flexing to underline Vladimir Putin's support for Mr Lukashenko who has held office for 26 years.
North Atlantic Treaty Organisation and European leaders have urged Lukashenko to launch a dialogue with the opposition, and respect the fundamental human rights of Belarus' citizens.
'I can not, I have no right to abandon the Belarusians, ' he said.
After polls closed, thousands of Belarusians took to the streets to protest the results, considered by many to have been fixed.
Lukashenko has bristled at suggestions of dialogue with the opposition.
The government did not publicise time and location of the inauguration ceremony in advance.
On Wednesday, German government spokesman Seibert said that Germany supported activating sanctions against Belarusian officials as soon as possible, adding Berlin regrets that the EU's foreign ministers have yet to agree. Amid worldwide outrage over the violent crackdown on the protests, Belarusian authorities switched to prosecuting top activists.
The EU again threw its full support behind the peaceful Belarus protests and their calls for new elections "despite the brutal repression of the Belarusian authorities", he said.
Fellow opposition figure Olga Kavalkova called the inauguration a "pathetic circus", accusing Lukashenko of "clinging to power and threatening his own people".
Defense Minister Viktor Khrenin read out the text of the oath: "We, military personnel of army units of the Republic of Belarus, assure the entire Belarusian nation and you, comrade commander-in-chief, that we are always ready to reliably protect the sovereignty and territorial integrity of our Motherland. An unfortunate error of history and a disgrace of the civilized world", Latushko said on the messaging app Telegram.